A set of maven-enforcer-plugin rule

relative path to parent

If a project is referring to a parent pom, but that pom isn't reachable in the default parent path (../pom.xml). Then you should either :

update it to the right path

put <relativePath /> in the <parent> tag so that maven knows it will have to look for it directly in the local repository

Standard variables

For example, when one wants to refer to the artifactId of a POM, the variable ${project.artifactId} can be used.
There are a lot of other possibilities to do that, like ${pom.artifactId}, ${artifactId} and so on.
These ways are all deprecated and might be deleted in the future. With maven3, all these deprecated uses appear as warnings.